Ok everyone, a little update here. I was never able to figure out the interupt for all my attempts. I ended up removing all references to the interupt alltogether. Instead now, at the end of every PWM loop, a quick check is done to see if the RI1 bit it set (and if a byte was receieved) - if it was a sub is executed to determine for which coordinate the byte received is.
The data being sent is basically X, 128, Y, 128. Im using a variable (yes, R2) to keep track of the information. When an "X" is received it should set R2 to #1, so the next time a byte is received, the system knows it should be the X coordinate. When running this program, some of the picture to be drawn is easily recognizable, the other half is just garbage. This probably comes from the uC simply not being fast enough. I'm going to replace the crystal and make some small changes and speed it up. It could also be the serial port just isn't fast enough. I may look into some type of USB transmission system - but I'm not sure where to begin.